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The KMOS Deep Survey (KDS) I: dynamical measurements of typical star-forming galaxies at z $\simeq$ 3.5

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(2017)cite arxiv:1704.06263Comment: main body 25 pages, 8 figures.

Abstract

We present dynamical measurements from the KMOS (K-band Multi-Object Spectrograph) Deep Survey (KDS), which is comprised of 77 typical star-forming galaxies at z $\simeq$ 3.5 in the mass range 9.0 < log(M$_\star$/M$_ødot$) < 10.5. These measurements constrain the internal dynamics, the intrinsic velocity dispersions (\sigma$_int$) and rotation velocities (V$_C$) of galaxies in the high redshift Universe. The mean velocity dispersion of the galaxies in our sample is \sigma$_int$ = $70.8^+3.3_-3.1$ km s$^-1$, revealing that the increasing average \sigma$_int$ with increasing redshift, reported for z $łesssim2$, continues out to z $\simeq$ 3.5. Only 34 $\pm$ 8% of our galaxies are rotation-dominated (V$_C$/\sigma$_int$ > 1), with the sample average V$_C$/\sigma$_int$ value much smaller than at lower redshift. After carefully selecting comparable star-forming samples at multiple epochs, we find that the rotation-dominated fraction evolves with redshift with a z$^-0.2$ dependence. The rotation-dominated KDS galaxies show no clear offset from the local rotation velocity-stellar mass (i.e. V$_C$-M$_\star$) relation, although a smaller fraction of the galaxies are on the relation due to the increase in the dispersion-dominated fraction. These observations are consistent with a simple equilibrium model picture, in which random motions are boosted in high redshift galaxies by a combination of the increasing gas fractions, accretion efficiency, specific star-formation rate and stellar feedback and which may provide significant pressure support against gravity on the galactic disk scale.

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